1. Field of the Invention
The present invention relates to an improvement of an ignition system for an internal combustion engine of an automotive vehicle having a plurality of engine cylinders, wherein a voltage boosting means is provided for boosting a low DC voltage into a high DC voltage, a high-voltage withstanding capacitor is provided for a spark plug within each engine cylinder so as to charge the boosted high DC voltage, and operatively supplies the charged high DC voltage via a boosting transformer into the corresponding spark plug as a discharge energy at a predetermined ignition timing, the amount of discharge energy changing according to various engine operating conditions so as to provide an appropriate amount of ignition energy for each spark plug.
2. Description of the Prior Art
A conventional ignition system comprises: (a) a low DC voltage supply such as a vehicle battery; (b) an ignition coil having a primary winding and secondary winding, one end of the primary winding being connected to the plus electrode of the low DC voltage supply and the other end of the primary winding being connected to one end of the secondary winding; (c) a contact point which opens and closes in synchronization with the engine revolution, one end of contact point being connected to the common end of both primary and secondary windings and the other end being grounded; and (d) a distributor having fixed contacts and a rotor, the rotor being rotated in synchronization with the engine revolution and being brought in contact with one of the fixed contacts sequentially one rotation of the rotor corresponding to one engine cycle, and each fixed contact being connected to a corresponding spark plug within one of the engine cylinders via a high-tension cable.
In such a construction described above, when a DC current flowing through the primary winding of the ignition coil from the low DC voltage supply is interrupted by the contact point, a high surge voltage having a peak value of several ten kilovolts is produced at the secondary winding thereof. The high surge voltage is applied to the distributor. The distributor distributes the high surge voltage into one of the spark plugs when the rotor comes in contact with the corresponding fixed contact.
However, such a conventional ignition system has a drawback that the transmission loss from the low DC voltage supply to the spark plugs is as large as, e.g., 80 to 90 percent of the power that the battery of the low DC voltage supply provides, and inductive energy at the primary winding of the ignition coil cannot be varied according to the engine operating condition. Therefore, the ignition energy cannot easily be varied according to the engine operating condition so that total power consumption increases. On the other hand, if the ignition energy is decreased by, e.g., reducing the inductance of the ignition coil so as to save total power consumption, a stable combustion cannot be achieved in the case of lean air-fuel mixture ratio (A/F.gtoreq.18).